The use of copper alloys as wiring material substitutes for conventional aluminum alloys is advancing, with the aim of increasing the performance of LSI. Copper alloys are poorly suitable for micromachining by dry etching which is often used for forming conventional aluminum alloy wiring. The “damascene method” has therefore been largely employed for micromachining of copper alloys, in which method a copper alloy thin-film is accumulated on an insulating film having pre-formed furrows (concave portions) and elevated sections (convex portions) to embed the copper alloy in the furrows, and then the copper alloy thin-film accumulated on the elevated sections (the copper alloy thin-film on sections other than the furrows) is removed by CMP to form embedded wiring (see Patent document 1, for example).
The common method of CMP for metals such as copper alloys involves attaching a polishing cloth (polishing pad) onto a circular platen, wetting the polishing cloth surface with a polishing agent for metals, pressing the metal film-formed surface of a base substrate against the polishing cloth surface, rotating the platen with a prescribed pressure (hereunder referred to as “polishing pressure”) being applied to the metal film from the back side of the base substrate, and removing the metal film on the elevated sections by mechanical friction between the polishing agent and the metal film on the elevated sections.
A polishing agent for metals used for CMP usually comprises an oxidizing agent and a solid abrasive (hereunder referred to simply as “abrasive”), with a metal oxide solubilizer, protective film-forming agent and the like if necessary. The basic mechanism of CMP employing a polishing agent comprising an oxidizing agent is considered to be that the metal film is polished by, first, oxidizing the metal film surface with the oxidizing agent to form an oxidation layer, and shaving of the oxidation layer with the abrasive.
In this polishing method, since the oxidation layer on the metal film surface of the furrows of the insulating film is not significantly contacted by the polishing cloth and is not reached by the shaving effect of the abrasive, the metal film on the elevated sections is removed as CMP proceeds, thus smoothing the base surface (see Non-patent document 1, for example).
In ordinary manufacturing of an LSI, the film thickness of the copper alloy film to be polished is about 1 μm, and a polishing agent which allows a polishing speed of about 5000 Å/min is used (see Patent document 2, for example).
In recent years, CMP treatment of copper alloys is being applied for manufacture of high performance microcircuit boards such as package boards, and for the formation of Through Silicon Vias (TSV) that have become an object of interest in new mounting methods.
However, the metal film thicknesses are larger for such purposes compared to LSIs, and therefore problems of low polishing speed and reduced productivity occur with conventional LSI polishing agents. TSVs, in particular, commonly require polishing of copper alloy films with film thicknesses of 5 μm or greater and sometimes 10 μm or greater, and therefore polishing agents that allow higher polishing speeds are desired.
Patent document 3 thus discloses a polishing agent which allows polishing of copper alloy films at polishing speeds that are higher than the prior art (about 22000-29000 Å/min).